1. Field of the Invention
The present invention relates to improving the inverter apparatus used to control an AC motor.
2. Description of the Related Art
The inverter apparatus which drives an AC motor detects the currents for the respective phases output from the inverter apparatus to the AC motor, then feeds them back to effect feedback control for current. With the inverter apparatus that is mounted to a three-phase AC motor, for example, current detectors are incorporated to detect the respective currents of two phases and thereby perform feedback control for the respective current phases.
In the above case, if a difference in gain occurs between the current detectors, torque ripple will occur, resulting in unstable rotation of the AC motor. The conventional way to deal with this problem is to adjust the gain unbalance for each inverter apparatus before the apparatus is turned on or while it is operating, either manually or automatically, based on values detected by the current detectors of the inverter apparatus, or data on motor speed, position and torque. Refer to Japanese Patent Application Laid-open No. H6-121569 for an example.
With the conventional technology, in order to compensate for gain unbalance in the current detectors of the inverter apparatus, either before the inverter is turned on, or while it is operating, measures need to be taken, such as rotating the motor or allowing the output current in the inverter apparatus to flow. Also, the gain unbalance needs to be readjusted when the inverter apparatus is replaced and the replaced inverter apparatus is connected to a motor or current detectors.